Design Of Frequency Selective Surface Research Articles

Dual‐band sub‐6‐GHz frequency filtering with optically transparent single‐layer dual‐polarized smart surface

AbstractOptically transparent dual‐band frequency‐selective surfaces (FSSs) are promising candidates to address the specific design challenges of the Internet of Things. This paper demonstrates their potential by discussing different configurations of the two single‐layer FSS designs on an innovative optically transparent polyvinyl chloride surface material. First, FSS cells consist of two cross dipoles placed forming angles of , where each rotated dipole structure parallel to the other. Then, in the second design, each one of the two cells is mirrored to enable polarization control for each band. As a proof‐of‐concept, five prototypes of each design having a unit cell size of are fabricated through a combination of cost‐effective printing and shearing. The manufactured prototypes yield more than 93% transparency and robust dual‐band performance. Moreover, more than 20 and 40 dB isolation for lower‐ and upper‐frequency bands are achieved from the fabricated prototypes. High‐transparency, cost‐effectiveness, and robust high performance in terms of suppression make both structures suitable for sub‐6‐GHz fifth generation applications.

Angular Stability Enhancement Using Phase Compensation Method for Frequency Selective Surface Design

This study introduces a novel phase compensation-based, asymmetric frequency selective surface (FSS). Aimed at enhancing angular stability, the phase compensation method utilizes the reflected phase gradient changes generated by two FSSs at large grazing angles. The ultimate improvement in angular stability comes from unit amalgamation to achieve phase complementarity, effectively dealing with the phase shift of incident waves caused by large grazing angles. Based on this principle, the asymmetric FSS structure is built with 3 components: a Minkowski fractal cell, a bent-line square-loop cell, and a thin square-loop parasitic cell. Simulation results show the structure demonstrates a 0 relative shift of resonant frequency within an incidence range of 0-80° under transverse electric (TE) polarization. However, it exhibits a maximum relative shift of 5.12% in resonant frequency at an 80° incidence under transverse magnetic (TM) polarization. Compared with E 1 and E 2 units, this structure significantly reduces frequency deviation—by 100% at 80° incidence under TE polarization and by 80.12% and 83.26% compared with E 1 and E 2 units under TM polarization. Finally, the proposed FSS model was fabricated and processed, with measured data basically aligning with the simulated results.

COMPARATIVE ANALYSIS OF EMBROIDERY AND SCREEN-PRINTING TECHNIQUES FOR TEXTILE-BASED FREQUENCY SELECTIVE SURFACES

Frequency Selective Surface (FSS) is a specialized structure used in the field of electromagnetic waves and radio frequency (RF) engineering. It is designed to exhibit selective transmission or reflection properties based on the frequency of the incident electromagnetic waves. This article describes the design, construction, and analysis of a textile-based band-stop frequency selective surface for use in the highly EM-polluted GSM, Wi-Fi, LTE, and WiMAX bands. A full-wave EM solver called CST Microwave Studio was used to develop and simulate the unit cell of the proposed FSS at the relevant frequency. In this study, embroidered and screen-printed textile based FSSs were designed. According to the results of this study, it was demonstrated that both embroidery and screen printing FSSs exhibit resonance at a frequency of 3.5 GHz. The screen printing method yielded the best results in terms of resonance frequency sensitivity, while the embroidery method showed a resonance frequency shift. It was observed that the stitch directions and density are important parameters in the embroidery method. Gaps between the embroidery paths in the production of embroidered FSSs resulted in differences from simulations due to the disruption of the structural integrity of the unit cell. Consequently, textile-based FSSs offer advantages over traditional FSSs. This study highlights the potential of textile FSSs as an effective means of reducing electromagnetic pollution, and suggests that further improvements in the design and production processes of textile FSSs can be made.

Design of a single layer single band 5G FSS as shielding materials

This paper deals with a novel Frequency Selective Surface (FSS) Electromagnetic shield that operates in the low 5G vertical applications. This FSS is designed for the purpose of serving as an electromagnetic shield to eliminate EMI. The FSS designed operates at a frequency of 5GHz with a bandwidth of 1.45GHz providing a shielding of more than 40dB. The proposed FSS uses a polyester sheet as substrate and uses silver for the metallization of the FSS. Since the proposed FSS is symmetric, it behaves similarly when a Transverse Electric (TE) or a Transverse Magnetic (TM) wave is incident. The structure was designed and simulated using CST software. The results show that this FSS blocks electromagnetic radiation at lower frequencies as intended.

Design of Wideband Frequency Selective Surface Based on the Combination of the Equivalent Circuit Model and Deep Learning

In this letter, a design method for frequency selective surface (FSS) based on the equivalent circuit model (ECM) and deep learning is proposed. In the proposed method, the ECM depicting the target transmission characteristic is first established. Then, with the aid of the established ECM, the target transmission characteristic is converted into the desired transmission curve and the initial topology of the FSS structure is determined. The cascade network is adopted to realize the rapid inverse design of the FSS structure. Benefiting from the established ECM, the high quality of the training data and proper description of the design target can be ensured in deep learning. For verification, an ultra-wideband FSS structure with a passband ranging from 3.1 to 12.05GHz and a stopband ranging from 12.85 to 20GHz is designed. Both simulated and experimental results show that the designed FSS provides an ultra-wide passband with flat-top and fast roll-off characteristics, covering 98.9% target passband and 95.3% target stopband.

A Switchable A-T-A Rasorber With Polarization Selectivity and High Roll-Off Characteristics

Switchable rasorber has attracted a great deal of interest in recent years due to its in-band shielding ability. In this work, a methodology for designing a switchable rasorber with high roll-off and polarization selection characteristics is proposed. The device can be switched between rasorber, polarization selection and absorber modes, and composes of two resistive layers (a passive and an active resistive layer) and a frequency selective surface (FSS). Transmission zeros (TZs) are introduced in the FSS design to improve the roll-off characteristic of its transmission band. The PIN diodes on the active resistive layer and FSS can be independently controlled in the orthogonal polarizations to realize the polarization selectivity. The simulation results indicate that the device exhibits a 27.5% fractional transmission bandwidth (3.42 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\sim$</tex-math></inline-formula> 4.51 GHz) under rasorber mode. In addition, the fractional absorption bandwidth is as large as 142.9% (1 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\sim$</tex-math></inline-formula> 6 GHz) under absorber mode. A prototype is fabricated and measured to validate the proposed design methodology. This work is promising for designing metamaterials (MMs) with excellent flexibility and high performance.

Novel Dual Band Frequency Selective Surface and its Applications on the Gain Improvements of Compact UWB Monopole Antenna

In this work, a highly directional ultra-wideband (UWB) microstrip patch antenna as a single-element is suggested. The proposed antenna’s gain is enhanced with a novel dual-band frequency selective surface (FSS) placed beneath it. The FSS design has a hexagonal structure with meander line inductances and a capacitance-like structure connecting all of the corners to the middle. There is no metallic layer on the other side of the substrate, which shows transmission zeros at 4.95 GHz and 12.7 GHz, and a modified U-shaped monopole antenna is developed. First, the performance characteristics of the antenna and FSS are analyzed from the simulation results, and they are validated experimentally after fabrication, followed by measurement. The compact configuration comprises an antenna loaded with the proposed FSS results S11 less than -10 dB from 3.15 GHz to 22.65 GHz, covering the UWB band together with the X, Ku-band with a bandwidth of 19.5 GHz (151.16% FBW). The antenna’s overall physical dimensions would be 38.8 mm×38.8 mm×25.2 mm (0.407λo×0.407λo×0.265λo), with λo denoting the lowest frequency’s free-space wavelength. The FSS loading results in a 9.9 dBi maximum gain at 10 GHz. The antenna’s small size increases bandwidth, and its high peak gain makes it ideal for use in real-time applications.

Miniaturized frequency‐selective surface with reduced number of metallic vias for electromagnetic shielding

SummaryA miniaturized frequency‐selective surface (FSS) for radio frequency (RF) filtering applications is reported in this paper. The proposed FSS is designed to operate with band stop property at 1.57 GHz. The FSS element is developed using highly convoluted lines running on either side of the substrate interconnected using via lines. This specific arrangement increases the electrical length of the resonator without increasing the physical size. Furthermore, the stability towards polarization variation and independence to different angles of incidence are other major concerns in the design of FSS. The FSS unit cell has rotational symmetry thereby providing polarization‐independent operation. The angular independence is tested for various incidence angles, and the results are presented. The performance of the FSS is validated in real time, and the results are presented. The maximum realized transmission loss is 27 dB at 1.57 GHz, and the attenuation bandwidth with reference 10 dB shielding level is estimated to be 400 MHz centered around 1.57 GHz. The convolution technique along with shorting vias has offered this extreme miniaturization ranging from 7% to 95.7% with reference to most of the FSS reported for L‐band services such as radio, telecommunications, military, and aircraft surveillance.

Miniaturised element frequency selective surface design for high power microwave applications

AbstractA third‐order miniaturised element frequency selective surface (MEFSS) for high‐power microwave (HPM) systems is proposed. The MEFSS design is characterised by the excellent capability to handle high‐power waves and the stable frequency response at large incidence angles. Through combining the particle swarm optimisation algorithm and the equivalent circuit method to improve the efficiency, the design has low resonant temperature while maintaining a low maximum field enhancement factor. A theoretical guide for the selection of substrate parameters in high‐power systems is provided. Instead of being as small as possible, the loss tangent should be properly selected to reach a balance between metal loss and dielectric loss. To the author's best knowledge, it is the first time in‐band low temperature and out‐of‐band high temperature suppression at various incidence angles are realised. The results show that the frequency response remains stable for incident angles up to 60°, and the maximum temperature is reduced from 148°C to 44°C for incident power density of 10 kW/m2. A MEFSS prototype was fabricated, and the transmission coefficients were measured. The full‐wave simulation and measurement results agree well. It has significance to the engineering progress of FSS as radomes for HPM antenna systems.

A specialized partial discretized optimization algorithm for SLL suppression in FSS design

Side Lobe Level (SLL) suppression is a challenging but essential part of frequency selective surface (FSS) structural design. The SLL of the radiation pattern is a key parameter demonstrating the directional anti-interference ability and mainly depends on the geometry of the FSS. However, the correlation between SLL and FSS structural parameters is extremely complicated. A minor FSS structure change may result in a drastic diversion in the sidelobe’s direction or level, making the SLL the most difficult parameter to optimize. In this paper, an efficient optimization method specifically for SLL suppression is proposed. We discretized the edges of split square ring FSS structures by binary representation and generated new patterns based on the genetic algorithm. Optimization results showed that in the most optimal structure, the SLL was −23.41 dB, exhibiting a 5.17 dB reduction. Meanwhile, the center frequency variation was less than 2%. Moreover, the computation time cost was reduced by over 90% compared with that of the fully discretized pattern optimization method, showing that this novel method was truly effective in getting SLL suppressed FSS structures.

Miniaturization of a Fully Metallic Bandpass Frequency Selective Surface for Millimeter-Wave Band Applications

This article presents a miniaturized all-metallic bandpass frequency selective surface (FSS) for millimeter-wave (mmWave) applications. The designed FSS is realized as a slot-type element that can be easily incorporated into all-metallic device architectures. The miniaturization is achieved by a convoluted or meander slot structure, i.e., a miniaturization technique borrowed from conventional substrate-based FSS design. It is demonstrated that the proposed FSS element provides a stable and wide bandpass performance from 24.9 to 31.4 GHz for both the transverse electric (TE) and the transverse magnetic (TM) polarizations at the broadside direction ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\theta = 0^{\circ }$</tex-math></inline-formula> ). Adequate performance is maintained at oblique incidence angles up to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\theta = \pm \,45^{\circ }$</tex-math></inline-formula> . A 25 × 25-elements FSS array prototype has been manufactured using the cost-effective chemical etching technique and experimentally characterized utilizing a free-space measurement setup. The results demonstrate a remarkably good correlation between simulations and measurements. Hence, the proposed miniaturized FSS represents an excellent potential to realize an all-metallic FSS with low insertion loss, low profile, and wideband performance at low fabrication costs for mmWave applications.

A novel dataset sampling method for deep learning-based absorption prediction of FSS absorbers

Combining the deep learning (DL) model to design frequency selective surface (FSS) is a promising research topic, while the DL model usually requires massive datasets. In order to reduce the size of the dataset while maintaining the performance of the DL model used to predict absorptivity of FSS absorbers, a novel dataset sampling method is proposed. Based on the bounded-loss theory, it is proposed that the performance of the DL model is determined by the sampling density and the difference between absorptivity of neighboring samples. This difference is measured by the variations of absorptivity corresponding to these samples. The absorptivity are acquired through the equivalent circuit model (ECM) analysis instead of full-wave simulation to provide immediate results during the sampling period. Numeric validations of the single-layer absorber show that the method requires a much smaller dataset size than the conventional random sampling method with the same Mean Square Error performance of the DL model. The three-layer results show that the method is more accurate in predicting the absorption rate when trained with 20% of the total dataset compared to the random method and the ECM method.

Model analysis of embroidered FSS and evaluation of production

This article presents the design, fabrication, and analysis of a textile-based band-stop frequency selective surface (FSS), in GSM, Wi-Fi, LTE, and WiMAX bands where the electromagnetic (EM) pollution is intense. The unit cell of the proposed FSS has been designed and simulated via a full-wave EM solver; CST Microwave Studio at the frequency of interest. In this study, embroidered textile-based FSSs were designed as an alternative to conventional FSSs. In the study, high textile detailed (from thread to embroidery direction) modeling was performed and the results of the modeling and experiments were compared. The results of this study showed that the embroidery direction has a dramatic effect on the electromagnetic behavior of the FSS. Both experimental and high textile detailed modeling results indicated that vertical or horizontal embroideries are not sufficient for band-stopping FSS. To overcome this problem, vertical-over-horizontal embroidery was used. The highly textile detailed model and its experimental results have proven that horizontal-over-vertical embroidery is successful in band-stopping FSS.

Convoluted Meander Line-Inspired Metallic Surface Filter for Bluetooth and WLAN Bands

A convoluted meander line integrated cross dipole metallic structure with a dual-bandstop feature is presented in this manuscript. The investigated frequency-selective surface (FSS) exhibits the bandstopping characteristics for the Bluetooth (2.4 GHz) and WLAN (5.5 GHz) applications with a miniaturized unit cell size of 9.7 × 9.7 mm2. The proposed design has a polarization insensitivity feature for the TE and TM polarized waves’ incidents at 0°–60° with an interval of 15° angle. The equivalent circuit model of the presented FSS unit cell is also discussed and their limped element values are presented. The FSS design has a compact size which makes it favorable for low-profile band-filtering systems and multipath EM wave’s insensitivity. The suggested FSS configuration has good correspondence with modelled and measured results.

Design and characteristic analysis of uniplanar multiband frequency selective surface for GSM, LTE, WLAN, ISM, WiMAX and X‐band applications

AbstractThe uniplanar compact, affordable, and unique slot‐based multiband frequency selective surface (FSS) of periodic cell size 0.14λc × 0.14λc (λc is wavelength at the initial stopband resonance) is presented in this article. The quadband FSS is analyzed using full‐wave simulation, circuit simulation (ECM), and experimental measurement where good agreement is attained. The FSS offers polarization independence with steady responses for all angular variations in the TE plane and up to 45° in the TM plane. The FSS offers dual stopbands at 2.75–4.15 and 9.45–12.48 GHz and dual passbands at 0.001–0.8 and 4.74–5.6 GHz that includes spectrum coverage of GSM, LTE, WLAN, ISM, WiMAX, and most part of X‐band communication.

Representation Learning-Driven Fully Automated Framework for the Inverse Design of Frequency-Selective Surfaces

Frequency-selective surfaces (FSSs) refer to planar structures that behave with specific electromagnetic (EM) responses within a frequency range and are widely applied in wireless propagation systems. Given the fact that different EM responses correspond to distinguished topologies, conventional inverse design methods of FSSs are usually labor-intensive, as they rely on experienced human engineers to determine the topology and then rationally tune its structures. There have been great attempts using optimization algorithms (e.g., genetic algorithms) or machine learning to automate the second tuning stage after the initial EM topologies are determined by human engineers. However, the first topology selection stage still requires engagements with experienced engineers. This article proposes a fully automated framework for the inverse design of FSSs. We achieved a fully automated inverse design by establishing a machine-friendly mapping flow. The mapping flow derives its continuity and compactness from representation learning, which enables both autoselection of the topology and autoevolution of the unit cell based on the topology. The autoselection stage automatically determines the appropriate topology by compressing the EM constraints through the principal component analysis (PCA) and classifying the topology using the support vector machine (SVM). Afterward, the autoevolution system can efficiently evolve until it yields an optimal unit cell. We developed a self-monitor strategy to control the evolution and maximize the evolution efficiency by adaptively tuning the three modules within the autoevolution system. We validated the presented framework with four FSS designs. The results proved its potential as a highly efficient fully automated tool for the inverse design of FSSs.

A Solution to the Dilemma for FSS Inverse Design Using Generative Models

Recently, artificial neural networks (ANNs) show a great potential in frequency selective surface (FSS) inverse design. However, it is inevitable to encounter the problem of non-unique mapping between inputs and outputs, which cannot be easily solved by the traditional ANNs framework. We analyze this existing dilemma from the perspective of information loss caused by data dimensionality reduction, and propose deploying generative models as a solution, for the first time. Specifically, two approaches with a novel model based on conditional Generative Adversarial Network (cGAN) are presented to achieve inverse design from the given indexes to FSS physical dimensions. By applying the proposed method, we can immediately obtain FSS design that meets the industrial demands without complex neural network processing or repeated iterations. Moreover, the proposed method is validated in closed-loop simulations and corresponding experiments, which also paves the way for designing complex FSS structures with desired electromagnetic responses using deep neural networks.

Design and Experimental Validation of a Switchable Frequency Selective Surface with Incorporated Control Network.

Tunable/switchable devices are more and more required in modern communication systems. However, the realization of the tuning requires the presence of active devices, which in turn must be biased. The current paper comes up with a solution for designing and experimentally validating such a switchable Frequency Selective Surface. Two different metallic structures are simulated and measured, having incorporated the same topology control network (CN). In this scenario, the main innovation of this paper is the presence of the feeding part, namely the control network. In this work, the main FSS structure is flanked by three parallel CN microstrip lines and several via holes that allow biasing the active elements, namely PIN diodes. The switchability of the proposed structure is achieved through PIN diodes, whose bias determines the values of the elements in the equivalent circuit. At different biases, the response of the FSS changes accordingly. From all possible values of the bias, the extreme cases when the diodes act as (almost) short- and open-circuits are considered in the submitted manuscript for the sake of brevity. These cases are modeled by the main and cut-slot structures, respectively. The proposed structures have been evaluated using electromagnetic simulation and implemented on an FR4 substrate having a thickness of 1.58 mm. With the periodicity of the square-shaped unit cell of 18 mm edge length, different filtering bands are obtained below 12 GHz. Another novelty that has received very little consideration in the existing literature is the use of a finite array of unit cells instead of an infinite one. And finally, tests in an anechoic chamber have proved that there is a good agreement between practical and simulation results and also demonstrated the proper performance of the devices for wide angular incidence for both TE and TM polarizations.

A modified Jerusalem inspired bandpass FSS for multiband applications based on concentric ring slots

Abstract This paper presents the design of a multi-band planar bandpass Frequency Selective Surface with the novel rings and a modified Jerusalem cross integrated structure. To begin, the proposed FSS array geometry is defined by constructing a unit cell size of order of 0.57 λ 0 × 0.57 λ 0 where λ 0 represents free-space wavelength of the first resonant frequency of the FSS periodic structure using novel concentric rings, leading to low profile design. The array structure is fabricated on the substrate material FR4 with a permittivity of 4.4 and having a thickness of 0.8 mm. Combination of concentric rings and Jerusalem Integrated Structure is examined. Low-profile, simpler design, improved angular and polarization stability are all benefits of the proposed FSS. The proposed FSS structure is designed to obtain a stable frequency response over entire Ku band. The simulated and experimental results are measured in a free space measurement setup, which indicate resonances at 12.39 GHz, 14.63 GHz, 16.11 GHz and 17.82 GHz, exhibits supported band pass frequency ratio 1.43 for Ku band applications. The simulated, equivalent circuit model and experimental results showed that the experimental results agree well with the simulated results for both TE (Transverse Electric) mode and TM (Transverse Magnetic) mode of polarization.

Low-Profile FSS Design Methodology to Increase Isolation between Vehicle-Borne Multifrequency Antennas

The present work describes a new approach for the design of a Frequency-Selective Surface (FSS) in the context of frequency filters to increase isolation between two vehicle-borne antennas. A compact FSS design based on nested square meandered resonators is optimized for multifrequency operation. Furthermore, a design workflow is proposed. In general, the measurement of low-profile FSS does not correspond to simulation through Floquet modes based on periodic boundary conditions due to the lack of uniformity of mutual coupling among the FSS unit cells. The proposed method demonstrates the agreement between the infinite simulation and the measurement of the finite prototype once a convenient scale factor is applied, which facilitates the design workflow. In this case, an FSS is used as an efficient filter to increase the isolation between antennas by 6 dB in three representative bands (3GPP, WiFI I and II). In this way, multifrequency antennas can be placed at approximately half their actual distance with the same performance in spatial-constrained vehicular environments.